Spark plug performance indicator



Nov. 28 1939. M. F PETERS ET AL 1 L SPARK PLUG PERFORMANCE KINDICA'IOR Filed April 25, 1939' 2 Sheets-Sheet l IN V E NTO RS 26 L147 WMQREN s. PARA? NELV/LLEF. PETERS BY H. KENDALL KIN NOV. 28, M, F. PETERS ET AL SPARK PLUG PERFORMANCE INDICATOR Filed April 25, 1959 2 Sheets-Sheet 2 ATTORNEY Patented Nov. 28, 1939 v UNITED STATES 2.181.149 SPARK PLUG PERFORMANCE INDICATOR Melville F. Peters, Beltsville, Md., Warren S.

Parr, United States Navy,

and Henry R. King,

Cabin John, Md. Application April 25, 1939, Serial No. 269,942

13 Claims.

(Granted under the act of amended April 30, 1928;

This invention relates generally to electrical ignition systemsof internal combustion engines and particularly to devices for indicating the performance of such systems. More particularly, it relates to devices for indicating the performance of spark plugs of aircraft engine ignition systems which are well shielded to prevent inter,- ference with radio reception.

It is well known in the art that if a pick-up voltage, obtained from a high voltage conductor connected to a spark plug of an internal combustion engine, isapplied across a sensitive voltage indicating means, such will show whether or not'the spark plug is firing properly.- It has likewise been shown that such pick-up voltage can be obtained by capacitive coupling to the said high voltage conductor.

But none of thedevices shown in the prior art is satisfactory for use in an aircraft equipped with sensitive radio receivingequipment, nor are such prior devices readily adaptable for use in connection with ignition systems present well-shielded aircraft which do permit satisfactory radio reception in the aircraft. e An object of our invention. is to provide an improved device for ,indicating the performance of ignition systems that is adaptable to the wellshielded ignition systems now in use in aircraft.

Another object of our invention is to provide an improved device for indicating ignition performance of aircraft internal combustion engines that is efiectively shielded to prevent ignition interference with radio reception. 5 A further object of our invention is to provide an improved device for indicating fouled ordefective spark plugs of aircraft engines in operation that permits effective radio reception in the aircraft in which the engine is installed.

With the above and other objects in view, the invention consists in the construction, combination and arrangement of parts as will be here-' inaftermore fully described.

Reference is to be had to the accompanying drawings forming a part of this specification in which like reference characters indicate corresponding parts-throughout the several views and in which:

Fig. 1 shows schematically our invention appliedto a well-shielded ignition conductor of an internal combustion engine;

Fig. 2 shows the device of Fig. 1 with the capacity relations indicated;

Fig. 3 shows the equivalent electrical circuit of all forms of our invention;

Fig. 4 is a longitudinal mid-sectional view terminal of voltage indicating March 3, 1883, as 370 0. G. 757) showing our invention as applied to a shielded ignition manifold of an internal combustion engine with a socket for plugging in a voltage indicating means;

Fig. 5 is a cross-sectional view of Fig. 4 5 through 5-5;

Fig. 6 is a mid-sectional view showing the shielded plug-in voltage indicating means, its connectors, and the plug which engages the socket of Fig. 4; and

Fig. '7 is a mid-sectional view showing our invention applied. to a shielded aircraft engine spark plug with a socket for plugging in a shielded plug connected to a voltage indicating means.

Referring to Fig. 1, an ignition conductor 8 connected to the ungrounded terminal of a spark plug 9 (not shown) is covered with suitable high voltage insulation l and is contained within grounded shield H. A conductive sheath I 2 sur- 20 rounds a portion of conductor 8, is a tight fit around the insulation l0 thereof, and is, of course, also contained within shield ll. Sheath i2 is connected to one terminal of voltage indicating means l3 by conductor I 4, the remaining means l3 being connected to ground. Conductor i4 is led through an openingin shield II and is surrounded by a shield I which is effectively bonded to shield II and is also connected to ground. 30 In Fig.2, the elements are the same as in Fig.

1 but the capacities between elements are indicated. In this figure, conductive'sheath l8 surrounds a portion of high voltage conductor [6 within grounded shield l1 and is connected, by

,meansof conductor ill, to one terminal of volt- I age indicating means 20, the remaining terminal I ductor l6 (Fig. 2) and sheath l8 (Fig. 2), or is 5 the summation of capacitors 22 (Fig. 2). Voltage indicating means 26, connected between one plate of capacitor 2 5 and ground, is obviously equivalent to the voltage indicating means of Figs. 1 and 2 connected between the conductive 5 sheath and ground. Capacitor 21 represents the capacity between sheath l8 (Fig. 2) and ground plus the capacity between conductor l9 (Fig. 2) and ground; or is the summation of capacitors 23 and 24 of Fig. 2. Conductor 25, shown connected to one plate of capacitor 25, corresponds to high voltage ignition conductors 8 and I6 of Figs. 1 and 2, respectively.

Figs. 4 and 5 illustrate an ignition manifold of. an internal combustion engine wherein a grounded cylindrical shield 24' surrounds a plurality of high voltage ignition conductors 26. A conductive sheath 26' is tightly clamped around the insulation 21'- of each conductor 26 and sheaths 26' are held rigidly in place in spaced insulating discs 21 which are a tight fit within cylindrical shield 24'. A shielding adapter 28 is clamped to either end of cylindrical shield 24 by means of threaded coupling nut 29. Each adapter 28 is bonded to a grounded shield through which conductors 26 pass in connecting distributor 3| (not shown) to spark plugs 30 (not shown) of the engine. A perpendicular integral cylindrical extension 3|, formed in the longitudinal wall of cylindrical shield 24', is externally threaded to receive detachable conductive cap 32. An insulating disc 33 containing a plurality of hollow cylindrical spaced contacts 33 is a tight fit inside cylindrical extension 3| to form a multi-contact socket 34'. A conductor 34 connects each sheath 26' to a separate contact 33'.

Referring to Fig. 6, an insulating disc 35, which fits tightly within a conductive shield 36, contains' a plurality of spaced conductive pins 31 and forms a plug 38 which is adapted to engage socket 34 of Fig. 4. An internally threaded nut 39 engages the externalthreaded portion of cylindrical extension -3|' (Fig. 4) when plug 38 engages socket 34' (Fig. 4), with cap 32 (Fig. 4) removed. Shield 36, circular in cross-section, has a reduced diameter portion 40, and, at the opposite end from plug 38, its diameter is enlarged to receive conductive disc 4| which supports a plurality of spaced neon bulbs 42, one for each conductor 26 (Fig. 4). An interior conductor 42'- connects each pin 31 to oneterminal of a neon bulb 42, the remaining terminal of each bulb 42 being grounded through disc 4| and shield 4|]. A transparent cover 43 permits visual observation of neon bulbs 42. Shield 36 is shown integral, but it may be made in several parts, with the reduced diameter portion 40 flexible, provided all parts are bonded to each other and effectively grounded.

In Fig. '1, conductive sheath 44 is tightly clamped around the insulation 45 of conductor 46 which is contained within the grounded shield 41 of the shielded aircraft engine spark plug shown. Sheath 44 is threaded to receive perpendicularly extending conductive stud 48, the other end of which engages hollow socket tube 49. A hollow cylindrical shield 56 is bonded to shield 41 and surrounds stud 48. Insulating spacers 5| and 52 hold stud 48 rigidly in place within cylindrical shield 50. A detachable conductive cap 53 engages the outer threaded portion of cylindrical shield 56. When the cap 53 is removed, a plug-in connector to a neon bulb or other voltage indicating means may be plugged in to socket tube 49.

As previously explained, Fig. 3 illustrates the equivalent electrical circuits of Figs. '1 and 2. Figs. 4, 5 and 6, with cap 32 (Fig. 4) removed and plug 38 (Fig. 6) plugged into socket'34' (Fig. 4) illustrate the application'of the device to Fig. 1 to a plurality of conductors 26 contained Within a shielded ignition manifold, with means for detachably plugging in the voltage indicating means. It is apparent that Fig. 3 also shows the equivalent circuit of any one of the several indicator circuits of Figs. 4, 5 and 6. Fig.1 shows the device of Fig. 1 applied to a shielded aircraft engine spark plug, with a plugin feature for the voltage indicating means similar to that of Figs. 4 and 6. Fig. 3 likewise represents the equivalent circuit of Fig. 7, with its voltage indicating means (not shown) plugged in.

Thus, referring to Fig. 3, which is the equivalent circuit of all forms of our device illustrated, when a high voltage is impressed between conductor 25' and ground, as occurs periodically when the particular spark plug to which conductor 25' is connected is energized in accordance with the timing of the engine, this high voltage is impressed across capacitors 25 and 21 in series, and is divided in accordance with the following well-known relations:

where I C1=the capacity of capacitor 25. C2=the capacity of capacitor 21. E1:the voltage impressed across capacitor 25. Ez=the voltage impressed across capacitor 21. E :the voltage impressed between conductor 25 and ground.

From the above it also follows that:

Since capacitor 21 and voltage indicating means 26 are in parallel, voltage E2 is likewise impressed across voltage indicating means 26.

-It is well known in the art that if the spark plug to which conductor 25 is connected is fouled, voltage E will be reduced below that value for normal operation of the engine. Other ignition troubles likewise manifest themselves by reduced voltage E, for example, weak or. frayed insulation on conductor 25, too small a gap between the sparking electrodes of the spark plug to which conductor 25' is attached, etc., while too great a gap between spark plug electrodes will manifest itself by an increased value of E. Since E2, the voltage impressed across the voltage indicating means 21, is directly proportional to E, it will change correspondingly, and voltage indicating means 21 will indicate the aforementioned spark plug or ignition troubles by a change of the reading or indication thereon.

The value of which determines the ratio Ez;E, may be varied to suit the particular voltage indicating means it may be desired to employ, by varying the value of C1 and C2. C1 may be varied by changing the length to achieve length of the sheath surrounding the ignition conductor. A minimum value of C2 is unavoidable, but, if desired, it may be arbitrarily increased by shunting an additional capacitor across the voltage indicating means 26 (Fig. 3). A certain degree of flexibility is thereby obtained which is useful in obtaining the desired value of E2 for a normally functioning spark plug.

It has been determined that ungrounded or incompletely grounded ignition shields, or shields grounded only through a voltage indicating means, such as a neon bulb, do not prevent excessive ignition interference with radio reception in an aircraft. In all present aircraft ignition shelding systems that eifectively prevent such ignition interference with radio reception, the shields are complete and well grounded. In some cases it has even been found necessary to ground the shield about ei?ry eighteen inches along its he object of good radio re- I ception. Thus, it cannot be too strongly stressed that adequate, well-grounded shielding is essential if successful radio communication is to be carried on in an aircraft equipped with an electrical ignition system. It will be noted that all forms of our invention utilize a well-grounded external shield and that our invention is employed only in connection with electrical ignition systems' employing grounded external shields.

The detachable plug-in features of the forms of our invention illustrated by Figs. 4, 5, 6 and 7,

give certain advantages of flexibility, in that the voltage indicating means may either be continuously installed or may be plugged in only when it is desired to check the spark plugs of a particular engine. If it is desired to utilize a particular type of voltage indicating means that is considered too fragile for continuous use in an operating aircraft, this particular type of voltage indicating means could be kept on the ground and could be detachably plugged in for test purposes. Also, by means of such a plug-in arrangement, a single voltage indicating means would serve for use with a number of engines equipped with the device illustrated by Figs. 4 and 5.

Any reasonably sensitive voltage indicating means can be employed with our invention. Fig. 6 shows the use of neon gas discharge bulbs and such have proved very satisfactory. With this type of voltage indicating means, by varying the capacity of Cl and C2 (Fig. 3), E2 can be made of such a value that for normal operation-of the spark plug it will just cause the neon bulb to glow. In such a case, failure of the bulb to glow would indicate a fouled plug (or one of the other ignition troubles aforementioned) and too bright a glow would indicate too great a sparking'gap at the sparking electrodes of the spark plug. By varying the values of C1 and C2, a wide range of values of E2 can be obtained as may be required for the particular type of voltage indicating means employed.

Another type of voltage indicating means that has been found especially adaptable for shop and laboratory use is the cathode ray oscillographl By its use, quantitative measurements of the ignition voltage can be obtained. By means of these measurements, approaching ignition failures can be detected before they actually occur and proper double banked air-cooled aircraft engines, in

fouled or defective plugs will cause a reduction in engine speed but it is very diflicult to determine which plug or plugs are defective. The task of removing, testing and examining all of the plugs, twenty-eight in number, of one of these engines is both diflicult and time consuming. By the use factured and/or used by or for the Government of the United States of America for governmental purposes without the royalties thereon or therefor.

We claim:

1. In combination, a high voltage conducting means connected to a spark plug of an internal combustion engine, a grounded voltage indicating means capacitively coupled to said conducting means, and an external. grounded shielding means for the above whereby a shunting capacitor to ground is formed across said voltage indicating means.

2. In combination, a high voltage internal conductor of a spark plug of an internalcombustion engine, a grounded voltage indicating means capacitively coupled to said conductor, and an external grounded shielding means for the above whereby a shunting capacitor to ground is formed across said voltage indicating means.

3. In combination, a high voltage ignition conductor of an internalcombustion engine, a conducting sheath surrounding a portion of said high voltage conductor, an external grounded shielding means for said high voltage conductor and said sheath, a voltage indicating means, a grounding means for said voltage indicating means, a conducting means connecting said sheath to said voltage indicating means, and a grounded shielding means for said conducting means.

4. In combination, a high voltage ignitionconductor of an internal combustion engine, a conducting sheath surrounding a portion of said high voltage conductor, an external grounded shielding means for said high voltage conductor and said sheath, a voltage indicating means, a grounding means for said voltage indicating means, a socket means with a detachable plug means therefor, a conducting means connecting said sheath to said voltage indicating means through said socket means and said plug means, and a grounded shielding means for said conduct ing means.

5. In combination, a high voltage ignition conductor of an internal combustion engine, a conducting sheath surrounding a portion of said high voltage conductor, an *external grounded shielding means for said high voltage conductor and said sheath, a voltage indicating means, a grounding means for said voltage indicating means, a conducting means connecting said sheath to said voltage indicating means, and a grounded shielding means for said conducting means wherebysaid sheath is' capacitively coupled to said ignition conductor, and whereby said payment of any i sheath and said conductin means are capac" 7 tively coupled to the respective shielding means therefor. 6. In combination, a high voltage ignition conductor of an internal combustion engine, a conducting sheath surrounding a portion of said high voltage conductor, an external grounded Shielding means for said high voltage conductor and said sheath, a voltage indicating means, a grounding means for said voltage indicating means, a socket means with a detachable plug means therefor, a conducting means connecting said sheath to said voltage indicating means through said socket means and said plug means, and a grounded shielding means for said conducting means, whereby said sheath is capacitively coupled to said ignition conductor, and whereby said sheath and said conducting means are capacitively coupled to the respective shielding means therefor.

7. In combination, a high voltage internal conductor of a spark plug of an internal combustion engine, a grounded shielding means for said spark plug, a conductive sheath surrounding a portion of said internal conductor, said sheath being contained within said shielding means for said spark plug, a voltage indicating means, a grounding means for said voltage indicating means, a conducting means connecting said sheath to said voltage indicating means, and a grounded shielding means for said conducting means. a

8. In combination, a high Voltage internal conductor of a spark plug of an internal combustion engine, a grounded shielding means for said spark plug, a conductive sheath surrounding a portion of said internal conductor, said sheath being contained 'within said shielding means for said spark plug, a voltage indicating means, a grounding means for said voltage indicating means, a socket means and a detachable plug means therefor, a conducting means connecting said sheath to said-voltage indicating means through said socket means and said plug means, and a grounded shielding means for said conducting means.

9. In combination, a high voltage internal conductor of a spark plug of an internal combustion engine, a grounded shielding means for said spark plug, a conductive sheath surrounding a portion of said internal conductor, said sheath being contained within said shielding means for said spark plug, a voltage indicating means, a grounding means for said voltage indicating means, a conducting means connecting said sheath to said voltage indicating means, and a grounded shielding means for said conducting means, whereby said sheath is capacitively coupled to said internalconductor, and whereby said sheath and said conducting means are capacitively coupled to the respective shielding means therefor.

10. In combination, a high voltage internal conductor of a spark plug of an internal combustion engine, a grounded shielding means for said spark plug, a conductive sheath surrounding a portion of said internal conductor, said sheath being contained within said shielding means for said spark plug, a voltage indicating means, a grounding means for said'voltage indicating means, a socket means and a detachable plug means therefor, a conducting means connecting said sheath to said voltage indicating means through said socket means and said plug means, and a grounded shielding means for said conducting means, whereby said sheath is capacitively coupled to said internal conductor, and whereby saidsheath and said conducting means are capacitively coupled to the respective shielding means therefor.

11. In combination, a plurality of high voltage -ignition conductors of an ignition manifold of an internal combustion engine, a grounded external shielding means for said manifold, a conductive sheath surrounding a portion of each said ignition conductor of said manifold, said ignition conductors and said sheaths being contained within said grounded external shielding means, a plurality of voltage indicating means, a grounding means for said voltage indicating means, a conducting means connecting each said sheath to a separate voltage indicating .means, and a grounded shielding means for said conducting means.

12. In combination, a plurality of high voltage ignition conductors of an ignition manifold of an internal combustion engine, a grounded external shielding means for said manifold, a conductive sheath surrounding a portion of each said ignition conductor of said manifold, said ignition conductors and said sheaths being contained within said grounded external shielding means, a plurality of voltage indicating means, a grounding means for said voltage indicating means, a. socket means and a detachable plug means therefor, a conducting means connecting each said sheath to a separate voltage indicating means through said socket means and said plug means, and a grounded shielding means for said conducting means.

13. In combination, a plurality of high voltage ignition conductors of an ignition manifold of an internal combustion engine, a grounded external shielding means for said manifold, a conductive sheath surrounding a portion of each said ignition conductor of said manifold, said ignition conductors and said sheaths being contained within said grounded external shielding means, a plurality of voltage indicating means, a grounding means for said voltage indicating means, a conducting means connecting each said sheath to a separate voltage indicating means, and a groundedshielding means for said conducting means, whereby each said sheath is capacitively coupled to one said ignition conductor of said manifold, and whereby said sheaths and said conducting means are capacitively coupled to the respective shielding means therefor.

' MELVILLE F. PETERS.

WARREN S. PARR. HENRY K. KING. 

